The present invention relates to a sender assembly for a gauge. In particular, the present invention relates to a resistive element structure for a sender assembly of a gauge.
This invention relates to a gauge for measuring a liquid level. A common type of gauge is a float gauge that has a float that floats in the liquid being measured. Typically, the float is connected with other members of a sensor that move with the float as the liquid level changes. A common float gauge used for many years incorporates one variable resistor in the sensor to vary a resistance with a change in the liquid level. In such a sensor, a contact arm is moved along a resistive element as the float level changes. The resistance is measured between one end of the resistive element and the contact arm, which corresponds to the float position. The portion of the sensor incorporating the resistive element and the contact arm is commonly known as a sending unit or sender assembly.
U.S. Pat. No. 4,924,704 issued to Gaston discloses a fuel sender assembly having a float rod 22, a housing assembly 20 and 21, a resistor card 25, a carrier element 38, and a spring contact element 40. In particular, the resistor card 25 has one resistive film 55 disposed on a circuit card 54. One plurality of conductive strips 56 is laid down on the resistive film 55 to improve electrical contact between the resistive film and a spring contact end 41. The conductive strips 56 are elongated in a radial direction from a pivot point of a float portion 23. The conductive strips 56 have a variable width to provide gaps of constant size between each conductive strip 56, i.e., the sides of adjacent strips are parallel. Hence, the resistance between each conductive strip 56 is approximately the same.
U.S. Pat. No. 5,357,815 issued to Williamson discloses a gauge assembly 10 that uses a voltage divider circuit to provide a measurement of a fluid level within a tank or other environment. A pointer assembly 52 pivots about an axis 42 in response to a moving float 30 to indicate the fluid level. A plurality of contact arms 114, 116, 118 extending from a contact plate 58 on the pointer assembly 52 resiliently engage a point 120 along one resistive element 88. The first end of the resistive element 88 is connected to a voltage regulator 100, which is connected to a first wiper contact 94. The second end of the resistive element 88 forms a second wiper contact 96. The point 120 of contact between the contact arms 114, 116, 118, and the resistive element 88 is connected to an amplifier 102, which is connected to a third contact 95 to form a low impedance voltage divider.
U.S. Pat. No. 5,743,136 issued to Gaston, et al., discloses a fluid level sensor having one angular resistive element 110, and a float 24 coupled to one contact 44. The resistive element 110 is designed for use in conventional fuel level sensors having a float attached to an arm. The float 24 moves up and down with the fuel level, moving the contact 44 along a path 112. The resistive element 110 has a resistive layer and a conductive layer applied to an insulating substrate 111. The resistive layer includes a resistor material disposed in segments 114 disposed along the path 112. The segments 114 all contact a trim section 116. The conductive layer is disposed on top of the resistive layer. The conductive layer includes discrete pads 122, which are disposed coincidentally on the segments 114 of resistive material.
As disclosed in the prior art, there are many advantages to using a resistive element structure with discrete contact pads, such as providing discrete increments of resistance change as the float move with the liquid level. However, despite the widespread use, such prior art resistive element structures with discrete contact pads have a major disadvantage. By using only one resistive element and one row of discrete contact pads, the angular resolution of such prior art resistive elements is limited by the angular spacing between the discrete contact pads.
Therefore, a need exists for a resistive element of a gauge sensor that provides discrete increments of resistance change as a measuring member moves, as well as a high resolution of measurement.
The present invention has numerous advantages, such as providing higher angular resolution for a gauge in discrete increments as a measuring member moves. Another advantage is providing a substantially higher angular resolution in discrete increments without substantially increasing the size of the sender assembly to accommodate a longer wiper contact arm.
It is an object of the present invention to provide a resistive element structure for a gauge sensor that provides discrete increments of resistance change as a measuring member moves, while also providing a high angular resolution.
In accordance with one aspect of the present invention, a resistive element structure for a sender assembly of a gauge is provided. The resistive element structure comprises a first and second resistive element. A first set of contact elements is distributed along a first arc about a pivot point. Each contact element of the first set is electrically connected to the first resistive element. A second set of contact elements is distributed along a second arc about the pivot point. Each contact element of the second set is electrically connected to the second resistive element.
In accordance with another aspect of the present invention, a resistive element structure for a sender assembly of a gauge is provided. The resistive element structure comprises a first and second resistive element, each being formed on the structure. The first resistive element has a first elongated shape with a first longitudinal extent. A first plurality of contact elements is formed on a structure along a first arc at a first radial distance from a pivot point. A first set of leads extend from the first plurality of contact elements. Each lead of the first set of leads correspondingly connects each contact element of the first plurality of contact elements to the first resistive element. Each lead of the first set of leads connects to the first resistive element at a different location along the first longitudinal extent of the first resistive element. The second resistive element has a second elongated shape with a second longitudinal extent. A second plurality of contact elements is formed on the structure along a second arc at a second radial distance from the pivot point. A second set of leads extends from the second plurality of contact elements. Each lead of the second set of leads correspondingly connects each contact element of the second plurality of contact elements to the second resistive element. Each lead of the second set of leads connects to the second resistive element at a different location along the second longitudinal extent of the second resistive element.
In accordance with yet another aspect of the present invention, a gauge sensor is provided. The gauge sensor comprises a measuring member, a resistive element structure, and a contact carrier. The measuring member has a pivot portion, which is adapted to pivot about a pivot axis. The resistive element structure comprises a first resistive element, first plurality of contact elements, a first set of leads, a second resistive element, a second plurality of contact elements, and a second set of leads. The first resistive element is formed on the structure, is adapted to electrically connect to a gauge circuit, and has a first elongated shape with a first longitudinal extent. The first plurality of contact elements is formed on the structure along a first arc at a first radial distance from the pivot axis. Each lead of the first set of leads correspondingly connects each contact element of the first plurality of contact elements to the first resistive element. Each lead of the first set of leads connects to the first resistive element at a different location along the first longitudinal extent of the first resistive element. The second resistive element is formed on the structure, has a second elongated shape with a second longitudinal extent, and is adapted to electrically connect to the gauge circuit. The second plurality of contact elements is formed on the structure along a second arc at a second radial distance from the pivot axis. Each lead of the second set of leads correspondingly connects each contact element of the second plurality of contact elements to the second resistive element. Each lead of the second set of leads connects to the second resistive element at a different location along the second longitudinal extent of the second resistive element. The contact carrier is adapted to pivot about the pivot axis along with the pivot portion of the measuring member. The contact carrier has a first and second wiper contact. The first wiper contact is located at the first radial distance from the pivot axis, is adapted to electrically connect to at least one of the first plurality of contact elements as the measuring member pivots about the pivot axis, and is electrically connected to the gauge circuit. The second wiper contact is located at the second radial distance from the pivot axis, is adapted to electrically connect to at least one of the second plurality of contact elements as the measuring member pivots about the pivot axis, and is electrically connected to the gauge circuit.